Usually if dogs are mixed they have a white tip on their tail or white on their paws. A purebred lab will not have these. A purebred is all one color. You can look online for the exact specifications of the breed so that you can find other inconsistencies.
You never know - could be golden/yellow, chocolate, or even black. These are two different dog breeds.
Yes. All purebred Labradors should have a knot on the back of their head between the ears.
There are some rare instances where a purebred Singapura can be all black.
Not necessarily. Black abs are usually somewhere around 85 pounds. My black lab was 110 pounds (50 Kgs). He was also a purebred. He was not fat, just muscular and large framed. Some labs do just get that large.
Yes, a purebred Italian Greyhound can have a black coat.
Yes, a purebred Tornjak can have a black and tan coat.
You can't. The definition of a purebred dog is that his parents are known, and their parents are known and so on all the way back to when the breed was first defined. If you haven't got that you're SOL regardless of how nice your dog is and looks.
Take it to the vet
I don't think so. Beagles (if purebred) have a black spot on their tongue. Purebred chowchows have a purple tongue. I think it is just a purebred symbol. We had a rottweiler with black splotches on his gums, and he was purebred.
Yes, the purebred British Shorthair can have a black smoke coat.
Yes, a purebred Singapura can be black and white in color.
Sometimes they can have black or black spotted tongues. To be sure that your dog is a purebred contact the breeder and learn more about the sire and the dam. Possibly somewhere along the line your dogs ancestors could have chow in them... but your dog could also be just a purebred.